SPREKER
Raymond Knaapen, System engineer, TNO

TITEL
Equipment for atmospheric, spatial atomic layer deposition in roll-to-roll processes

TIJD

12:00

ABSTRACT
There are many types of thin film deposition techniques, such as Physical Vapour Deposition (PVD), Chemical Vapour Deposition (CVD) and Atomic Layer Deposition (ALD). ALD has a number of unique properties like high conformality to substrate topography, superior layer quality and thickness control down to Ångström level. The deposition rate, however, is very low in conventional ALD reactors (~1 nm/min), which makes cost-of-ownership high. To achieve high throughput and to reduce costs, there have been recent developments regarding spatial ALD, sometimes referred to as Fast ALD. Whereas in conventional ALD, precursors are dosed separated in time using a purge or pump step, in spatial ALD, precursors are dosed simultaneously and continuously at different physical locations. Because no purging step is needed in spatial ALD, the process can be operated at much higher speeds, limited by layer deposition chemistry rather than pumping times. Thus, deposition rates exceeding 1 nm/s have been reported for spatial atmospheric ALD of Al2O3. This has led to the development of high throughput, industrial scale ALD tools for surface passivation of crystalline silicon solar cells.
Substrates in existing ALD applications are usually flat and rigid, like silicon wafers or glass plates. Performing Fast ALD on these substrates involves e.g. cyclic movements of substrates or substrate rotation under a flat ALD injector head. Precursors are not allowed to come in contact with each other, other than on the substrate surface. Separation of precursors is achieved using gas bearing technology, which also enables small precursor chamber volumes.
Because of the increased throughput and decreased cost levels, new application fields are opening up for spatial ALD, such as flexible electronics, including system-in-foil, flexible displays, OLEDs and solar cells. Examples of layers are transparent oxide (semi)conductors (e.g. ZnO) and moisture permeation barriers (e.g. Al2O3).
For deposition on flexible substrates, a new type of atmospheric, spatial ALD reactor has been designed. Instead of a flat ALD injector head, a rotating drum is used to supply the precursor gases to slots at the peripheral surface of the drum, parallel to its rotation axis. A flexible substrate is transported around the drum surface, where gas bearings are used to separate the foil from the drum as well as separate the different precursors. The foil being contactless enables the drum to rotate at high speed while the foil is slowly advancing, such that every part of the foil surface will come into contact with a predefined number of precursor cycles. Each individual precursor pair cycle will deposit one monolayer of e.g. Al2O3. In the current design, the drum has six pairs of precursor slots at the outer surface. Thus, when the drum rotates at a frequency of 5 Hz, the number of precursor pairs per second is approximately 30, for low foil traversing speeds. When the foil covers 50% of the drum surface, an approximately 100 nm thick layer can be applied in a continuous roll-to-roll process. Such a layer can be used as e.g. A moisture barrier.
One of the challenges in the rotating drum design is the bearing of the foil around the drum. This bearing must ensure that the foil does not touch the drum and at the same time must separate the precursor gases. Other challenges are the gas supply to the rotating drum and interrupting the chemical reaction at the parts of the drum surface that are not covered with foil. Both issues are addressed using a contactless gas feedthrough at the flat sides of the drum. This feedthrough uses a similar gas separation method as used around the drum in the ALD deposition region.

BIOGRAFIE
Raymond Knaapen is afgestudeerd aan de TU Eindhoven in de sectie Dynamic Systems & Control in 1997. In 1999 heeft hij de ontwerpersopleiding Mechatronic Design aan het Stan Ackermans Institute afgerond, met als hoofdonderwerpen vermogenselektronica en elektromechanica voor het terugwinnen van energie. Daarna werkte Knaapen bij Philips Research en Philips Applied Technologies op het gebied van high-precision machinedesign voor verscheidene toepassingsgebieden zoals e-beam-microscopie, halfgeleiderfront-end, opticaproductie en robotica. In 2007 is Knaapen in dienst getreden bij TNO als senior system engineer op het gebied van mechatronica-apparatuur. Hij heeft gewerkt aan innovaties in halfgeleiderback-endsystemen en machines voor snelle atomic layer deposition (ALD).